Wireless device and method for receiving downlink control channel

ABSTRACT

An embodiment of the present description provides a method for receiving a downlink control channel by a wireless device. The method can comprise a step for, when a wireless device receives configuration for repetition of a downlink control channel, determining a plurality of subframes for receiving the repetition of the downlink control channel. A special subframe, on the basis of particular TDD special subframe configuration, can be determined to be excluded from the receiving of the repetition of the downlink control channel. The method can comprise a step for receiving the repetition of the downlink control channel on the determined plurality of subframes from which the special subframe has been excluded.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to mobile communication.

Related Art

3rd generation partnership project (3GPP) long term evolution (LTE) isan improved version of a universal mobile telecommunication system(UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE usesorthogonal frequency division multiple access (OFDMA) in a downlink, anduses single carrier-frequency division multiple access (SC-FDMA) in anuplink. The 3GPP LTE employs multiple input multiple output (MIMO)having up to four antennas. In recent years, there is an ongoingdiscussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPPLTE. [2] 3rd generation partnership project (3GPP) long term evolution(LTE) evolved from a universal mobile telecommunications system (UMTS)is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonalfrequency division multiple access (OFDMA) in a downlink, and usessingle carrier-frequency division multiple access (SC-FDMA) in anuplink. The 3GPP LTE employs multiple input multiple output (MIMO)having up to four antennas. In recent years, there is an ongoingdiscussion on 3GPP LTE-advanced (LTE-A) evolved from the 3GPP LTE.

As disclosed in 3GPP TS 36.211 V10.4.0 (2011-12) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 10)”, a physical channel of LTE may be classified into adownlink channel, i.e., a PDSCH (Physical Downlink Shared Channel) and aPDCCH (Physical Downlink Control Channel), and an uplink channel, i.e.,a PUSCH (Physical Uplink Shared Channel) and a PUCCH (Physical UplinkControl Channel).

Meanwhile, in recent years, research into communication between devicesor the device and a server without human interaction, that is, withouthuman intervention, that is, machine-type communication (MTC) has beenactively conducted. The MTC represents a concept in which not a terminalused by human but a machine performs communication by using the existingwireless communication network.

Since MTC has features different from communication of a normal UE, aservice optimized to MTC may differ from a service optimized tohuman-to-human communication. In comparison with a current mobilenetwork communication service, MTC can be characterized as a differentmarket scenario, data communication, less costs and efforts, apotentially great number of MTC devices, wide service areas, low trafficfor each MTC device, etc.

Meanwhile, in order to increase a penetration rate through reduction incost of an MTC device, a proposal that the MTC device should use only asubband of about 1.4 MHz, regardless of overall system bandwidth of acell, is under discussion.

This, however, has a problem that the MTC device cannot properly receivean existing PDCCH transmitted from a base station on the entire systemband.

Therefore, it is required to introduce a control channel for the MTCdevice to be transmitted within the subband in which the MTC deviceoperates.

The control channel to be newly introduced for the MTC device may be amodified form of the existing EPDCCH (Enhanced Physical Downlink ControlChannel). However, considering the TDD special subframe, there isdifficulty to define a new control channel by utilizing the existingEPDCCH as it is.

SUMMARY OF THE INVENTION

Accordingly, a disclosure of the present specification has been made inan effort to solve the aforementioned problem.

To achieve the foregoing purposes, the disclosure of the presentinvention proposes a method for receiving a downlink control channel.The method may be performed by a device and comprise: if the device isconfigured with a repetition of the downlink control channel,determining a plurality of subframes for receiving the repetition of thedownlink control channel. A special subframe based on a specific timedivision duplex (TDD) special subframe configuration is determined to beexcepted for receiving the repetition of the downlink control channel.The method may comprise: receiving the repetition of the downlinkcontrol channel on the determined plurality of subframes except for thespecial subframe.

A special subframe other than the excepted special subframe may bedetermined to be used for receiving the repetition of the downlinkcontrol channel.

The excepted special subframe may include a different number of enhancedcontrol channel elements (ECCEs) from a number of ECCEs of a normaldownlink subframe.

A special subframe other than the excepted special subframe may includedifferent numbers of enhanced resource element groups (EREGs) per a ECCEaccording to a cyclic prefix (CP) length.

The excepted special subframe may include one or more special subframeswith a special subframe configuration 1, 2, 6, 7 or 9 in normal CP.

The method may further comprise: receiving a system information block(SIB) for configuring the special subframe as a valid subframe.

If the special subframe is configured as the valid subframe, althoughthe special subframe is excepted for receiving the repetition of thedownlink control channel, the excepted special subframe may be used forcounting the number of valid subframes.

To achieve the foregoing purposes, the disclosure of the presentinvention proposes a device for receiving a downlink control channel.The device may comprise: a processor configured to determine a pluralityof subframes for receiving a repetition of the downlink control channel,if the device is configured with the repetition of the downlink controlchannel. A special subframe based on a specific time division duplex(TDD) special subframe configuration is determined to be excepted forreceiving the repetition of the downlink control channel. The device maycomprise: a transceiver controlled by the processor and configured toreceive the repetition of the downlink control channel on the determinedplurality of subframes except for the special subframe.

According to the disclosure of the present specification, the problemsof the above-described prior art are solved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a wireless communication system.

FIG. 2 illustrates a structure of a radio frame according to FDD in 3GPPLTE.

FIG. 3 illustrates a structure of a downlink radio frame according toTDD in the 3GPP LTE.

FIG. 4 is an exemplary diagram illustrating a resource grid for oneuplink or downlink slot in the 3GPP LTE.

FIG. 5 illustrates a structure of a downlink subframe.

FIG. 6. illustrates a structure of an uplink subframe in 3GPP LTE.

FIG. 7 illustrates an example of a subframe having an EPDCCH.

FIG. 8A illustrates an example of machine type communication (MTC).

FIG. 8B illustrates extension or enhancement of cell coverage for an MTCdevice.

FIG. 9 illustrates an example of transmitting a bundle of downlinkchannels.

FIG. 10a and FIG. 10b are examples of subbands for MTC device operation.

FIG. 11 shows one example of a control channel being transmitted in asubband for MTC device operation.

FIG. 12 is a flow chart illustrating a method according to thedisclosure of the present description.

FIG. 13 is a block diagram illustrating a wireless communication systemin which a disclosure of the present description is implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, based on 3rd Generation Partnership Project (3GPP) longterm evolution (LTE) or 3GPP LTE-advanced (LTE-A), the present inventionwill be applied. This is just an example, and the present invention maybe applied to various wireless communication systems. Hereinafter, LTEincludes LTE and/or LTE-A.

The technical terms used herein are used to merely describe specificembodiments and should not be construed as limiting the presentinvention. Further, the technical terms used herein should be, unlessdefined otherwise, interpreted as having meanings generally understoodby those skilled in the art but not too broadly or too narrowly.Further, the technical terms used herein, which are determined not toexactly represent the spirit of the invention, should be replaced by orunderstood by such technical terms as being able to be exactlyunderstood by those skilled in the art. Further, the general terms usedherein should be interpreted in the context as defined in thedictionary, but not in an excessively narrowed manner.

The expression of the singular number in the present invention includesthe meaning of the plural number unless the meaning of the singularnumber is definitely different from that of the plural number in thecontext. In the following description, the term ‘include’ or ‘have’ mayrepresent the existence of a feature, a number, a step, an operation, acomponent, a part or the combination thereof described in the presentinvention, and may not exclude the existence or addition of anotherfeature, another number, another step, another operation, anothercomponent, another part or the combination thereof.

The terms ‘first’ and ‘second’ are used for the purpose of explanationabout various components, and the components are not limited to theterms ‘first’ and ‘second’. The terms ‘first’ and ‘second’ are only usedto distinguish one component from another component. For example, afirst component may be named as a second component without deviatingfrom the scope of the present invention.

It will be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected or coupled to the other element or layer orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element or layer, there are no intervening elementsor layers present.

Hereinafter, exemplary embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.In describing the present invention, for ease of understanding, the samereference numerals are used to denote the same components throughout thedrawings, and repetitive description on the same components will beomitted. Detailed description on well-known arts which are determined tomake the gist of the invention unclear will be omitted. The accompanyingdrawings are provided to merely make the spirit of the invention readilyunderstood, but not should be intended to be limiting of the invention.It should be understood that the spirit of the invention may be expandedto its modifications, replacements or equivalents in addition to what isshown in the drawings.

As used herein, ‘base station’ generally refers to a fixed station thatcommunicates with a wireless device and may be denoted by other termssuch as eNB (evolved-NodeB), BTS (base transceiver system), or accesspoint.

As used herein, ‘user equipment (UE)’ may be stationary or mobile, andmay be denoted by other terms such as device, wireless device, terminal,MS (mobile station), UT (user terminal), SS (subscriber station), MT(mobile terminal) and etc.

FIG. 1 illustrates a wireless communication system.

As seen with reference to FIG. 1, the wireless communication systemincludes at least one base station (BS) 20. Each base station 20provides a communication service to specific geographical areas(generally, referred to as cells) 20 a, 20 b, and 20 c. The cell can befurther divided into a plurality of areas (sectors).

The UE generally belongs to one cell and the cell to which the UE belongis referred to as a serving cell. A base station that provides thecommunication service to the serving cell is referred to as a servingBS. Since the wireless communication system is a cellular system,another cell that neighbors to the serving cell is present. Another cellwhich neighbors to the serving cell is referred to a neighbor cell. Abase station that provides the communication service to the neighborcell is referred to as a neighbor BS. The serving cell and the neighborcell are relatively decided based on the UE.

Hereinafter, a downlink means communication from the base station 20 tothe UE 10 and an uplink means communication from the UE 10 to the basestation 20. In the downlink, a transmitter may be a part of the basestation 20 and a receiver may be a part of the UE 10. In the uplink, thetransmitter may be a part of the UE 10 and the receiver may be a part ofthe base station 20.

Meanwhile, the wireless communication system may be generally dividedinto a frequency division duplex (FDD) type and a time division duplex(TDD) type. According to the FDD type, uplink transmission and downlinktransmission are achieved while occupying different frequency bands.According to the TDD type, the uplink transmission and the downlinktransmission are achieved at different time while occupying the samefrequency band. A channel response of the TDD type is substantiallyreciprocal. This means that a downlink channel response and an uplinkchannel response are approximately the same as each other in a givenfrequency area. Accordingly, in the TDD based wireless communicationsystem, the downlink channel response may be acquired from the uplinkchannel response. In the TDD type, since an entire frequency band istime-divided in the uplink transmission and the downlink transmission,the downlink transmission by the base station and the uplinktransmission by the terminal may not be performed simultaneously. In theTDD system in which the uplink transmission and the downlinktransmission are divided by the unit of a subframe, the uplinktransmission and the downlink transmission are performed in differentsubframes.

Hereinafter, the LTE system will be described in detail.

FIG. 2 shows a downlink radio frame structure according to FDD of 3rdgeneration partnership project (3GPP) long term evolution (LTE).

The radio frame of FIG. 2 may be found in the section 5 of 3GPP TS36.211 V10.4.0 (2011-12) “Evolved Universal Terrestrial Radio Access(E-UTRA); Physical Channels and Modulation (Release 10)”.

The radio frame includes 10 sub-frames indexed 0 to 9. One sub-frameincludes two consecutive slots. Accordingly, the radio frame includes 20slots. The time taken for one sub-frame to be transmitted is denoted TTI(transmission time interval). For example, the length of one sub-framemay be 1 ms, and the length of one slot may be 0.5 ms.

The structure of the radio frame is for exemplary purposes only, andthus the number of sub-frames included in the radio frame or the numberof slots included in the sub-frame may change variously.

Meanwhile, one slot may include a plurality of OFDM symbols. The numberof OFDM symbols included in one slot may vary depending on a cyclicprefix (CP).

FIG. 3 illustrates the architecture of a downlink radio frame accordingto TDD in 3GPP LTE.

For this, 3GPP TS 36.211 V10.4.0 (2011-12) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, Ch. 4 may be referenced, and this is for TDD (timedivision duplex).

Sub-frames having index #1 and index #6 are denoted special sub-frames,and include a DwPTS (Downlink Pilot Time Slot: DwPTS), a GP (GuardPeriod) and an UpPTS (Uplink Pilot Time Slot). The DwPTS is used forinitial cell search, synchronization, or channel estimation in aterminal. The UpPTS is used for channel estimation in the base stationand for establishing uplink transmission sync of the terminal. The GP isa period for removing interference that arises on uplink due to amulti-path delay of a downlink signal between uplink and downlink.

In TDD, a DL (downlink) sub-frame and a UL (Uplink) co-exist in oneradio frame. Table 1 shows an example of configuration of a radio frame.

TABLE 1 Switch- UL-DL point Subframe index configuration periodicity 0 12 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 25 ms D S U D D D S U D D 3 10 ms  D S U U U D D D D D 4 10 ms  D S U U DD D D D D 5 10 ms  D S U D D D D D D D 6 5 ms D S U U U D S U U D ‘D’denotes a DL sub-frame, ‘U’ a UL sub-frame, and ‘S’ a special sub-frame.

When receiving a UL-DL configuration from the base station, the terminalmay be aware of whether a sub-frame is a DL sub-frame or a UL sub-frameaccording to the configuration of the radio frame.

TABLE 2 Normal CP in downlink Extended CP in downlink UpPTS UpPTSSpecial Normal Normal Extended subframe CP in Extended CP in CP inconfiguration DwPTS uplink CP in uplink DwPTS uplink uplink 0  6592 * Ts2192 * Ts 2560 * Ts  7680 * Ts 2192 * Ts 2560 * Ts 1 19760 * Ts 20480 *Ts 2 21952 * Ts 23040 * Ts 3 24144 * Ts 25600 * Ts 4 26336 * Ts  7680 *Ts 4384 * Ts 5120 * ts 5  6592 * Ts 4384 * Ts 5120 * ts 20480 * Ts 619760 * Ts 23040 * Ts 7 21952 * Ts — 8 24144 * Ts —

FIG. 4 illustrates an example resource grid for one uplink or downlinkslot in 3GPP LTE.

Referring to FIG. 4, the uplink slot includes a plurality of OFDM(orthogonal frequency division multiplexing) symbols in the time domainand NRB resource blocks (RBs) in the frequency domain. For example, inthe LTE system, the number of resource blocks (RBs), i.e., NRB, may beone from 6 to 110.

The resource block is a unit of resource allocation and includes aplurality of sub-carriers in the frequency domain. For example, if oneslot includes seven OFDM symbols in the time domain and the resourceblock includes 12 sub-carriers in the frequency domain, one resourceblock may include 7×12 resource elements (REs).

Meanwhile, the number of sub-carriers in one OFDM symbol may be one of128, 256, 512, 1024, 1536, and 2048.

In 3GPP LTE, the resource grid for one uplink slot shown in FIG. 4 mayalso apply to the resource grid for the downlink slot.

FIG. 5 illustrates the architecture of a downlink sub-frame.

In FIG. 5, assuming the normal CP, one slot includes seven OFDM symbols,by way of example.

The DL (downlink) sub-frame is split into a control region and a dataregion in the time domain. The control region includes up to first threeOFDM symbols in the first slot of the sub-frame. However, the number ofOFDM symbols included in the control region may be changed. A PDCCH(physical downlink control channel) and other control channels areassigned to the control region, and a PDSCH is assigned to the dataregion.

The physical channels in 3GPP LTE may be classified into data channelssuch as PDSCH (physical downlink shared channel) and PUSCH (physicaluplink shared channel) and control channels such as PDCCH (physicaldownlink control channel), PCFICH (physical control format indicatorchannel), PHICH (physical hybrid-ARQ indicator channel) and PUCCH(physical uplink control channel).

The control information transmitted through the PDCCH is denoteddownlink control information (DCI). The DCI may include resourceallocation of PDSCH (this is also referred to as DL (downlink) grant),resource allocation of PUSCH (this is also referred to as UL (uplink)grant), a set of transmission power control commands for individual UEsin some UE group, and/or activation of VoIP (Voice over InternetProtocol).

In 3GPP LTE, blind decoding is used for detecting a PDCCH. The blinddecoding is a scheme of identifying whether a PDCCH is its own controlchannel by demasking a desired identifier to the CRC (cyclic redundancycheck) of a received PDCCH (this is referred to as candidate PDCCH) andchecking a CRC error. The base station determines a PDCCH formataccording to the DCI to be sent to the wireless device, then adds a CRCto the DCI, and masks a unique identifier (this is referred to as RNTI(radio network temporary identifier) to the CRC depending on the owneror purpose of the PDCCH.

In 3GPP LTE, in order to decrease the load owing to the blind decoding,a search space is used. The search space may be referred to a monitoringset of CCE for the PDCCH. The UE monitors the PDCCH within thecorresponding search space.

When a UE monitors the PDCCH based on the C-RNTI, the DCI format and thesearch space which is to be monitored are determined according to thetransmission mode of the PDSCH. The table below represents an example ofthe PDCCH monitoring in which the C-RNTI is setup.

TABLE 3 Transmission Transmission mode of PDSCH mode DCI format Searchspace according to PDCCH Transmission DCI format 1A Public service andSingle antenna port, port 0 mode 1 terminal specific DCI format 1Terminal specific Single antenna port, port 0 Transmission DCI format 1APublic service and Transmit diversity mode 2 terminal specific DCIformat 1 Terminal specific Transmit diversity Transmission DCI format 1APublic service and Transmit diversity mode 3 terminal specific DCIformat 2A Terminal specific CDD (Cyclic Delay Diversity) or transmitdiversity Transmission DCI format 1A Public service and Transmitdiversity mode 4 terminal specific DCI format 2 Terminal specificClosed-loop spatial multiplexing Transmission DCI format 1A Publicservice and Transmit diversity mode 5 terminal specific DCI format 1DTerminal specific MU-MIMO(Multi-user Multiple Input Multiple Output)Transmission DCI format 1A Public service and Transmit diversity mode 6terminal specific DCI format 1B Terminal specific Closed-loop spatialmultiplexing Transmission DCI format 1A Public service and If the numberof PBCH transmisison mode 7 terminal specific ports is 1, single antennaport, port 0. Otherwise, transmit diversity DCI format 1 Terminalspecific Single antenna port, port 5 Transmission DCI format 1A Publicservice and If the number of PBCH transmisison mode 8 terminal specificports is 1, single antenna port, port 0. Otherwise, transmit diversityDCI format 2B Terminal specific Dual layer transmisison (port 7 or 8),or single antenna port, port 7 or 8 Transmission DCI format 1A Publicservice and Non-MBSFN sub-frame: if the mode 9 terminal specific numberof PBCH antenna ports is 1, port 0 is used as independent antenna port.Otherwise, transmit Diversity MBSFN sub-frame: port 7 as independentantenna port DCI format 2C Terminal specific 8 transmisison layers,ports 7-14 are used or port 7 or 8 is used as independent antenna portTransmission DCI 1A Public service and Non-MBSFN sub-frame: if the modeterminal specific number of PBCH antenna ports is 1, 10 port 0 is usedas independent antenna port. Otherwise, transmit Diversity MBSFNsub-frame: port 7 as independent antenna port DCI format 2D Terminalspecific 8 transmisison layers, ports 7-14 are used or port 7 or 8 isused as independent antenna port

The usage of the DCI format is classified as shown in Table 3 below.

TABLE 4 DCI format Contents DCI format 0 Used in PUSCH scheduling DCIformat 1 Used in scheduling of one PDSCH codeword DCI format 1A Used incompact scheduling of one PDSCH codeword and random access process DCIformat 1B Used in compact scheduling of one PDSCH codeword havingprecoding information DCI format 1C Used in very compact scheduling ofone PDSCH codeword DCI format 1D Used in precoding and compactscheduling of one PDSCH codeword having power offset information DCIformat 2 Used in PDSCH scheduling of terminals configured in closed-loopspatial multiplexing mode DCI format 2A Used in PDSCH scheduling ofterminals configured in open-loop spatial multiplexing mode DCI format2B DCI format 2B is used for resouce allocation for dual-layer beam-forming of PDSCH. DCI format 2C DCI format 2C is used for resouceallocation for closed-loop SU-MIMO or MU-MIMO operation to 8 layers. DCIformat 2D DCI format 2C is used for resouce allocation to 8 layers. DCIformat 3 Used to transmit TPC command of PUCCH and PUSCH having 2 bitpower adjustments DCI format 3A Used to transmit TPC command of PUCCHand PUSCH having 1 bit power adjustment DCI format 4 Used in PUSCHscheduling of uplink (UP) operated in multi-antenna port transmisisonmode

For example, a DCI format 0 will be described with reference to section5.3.3.1.1 of 3GPP TS 36.212 V10.2.0 (2011-06). The DCI format 0 includesa field as listed in a following table.

TABLE 5 Field Bit number Carrier indicator 0 or 3 bits Flag forformat0/format1A differentiation 1 bit FH (Frequency hopping) flag 1 bitResource block allocation and hopping resource allocation MCS(Modulation and coding scheme) and RV (redundancy 5 bits version) NDI(New data indicator) 1 bit TPC 2 bits Cyclic shift for DM RS and OCCindex 3 bit UL index 2 bits DAI (Downlink Allocation Index) 2 bits CSIrequest 1 or 2 bits SRS request 0 or 1 bit Resource allocation type 1bit

In the above table, the redundancy version (RV) is used for the HARQoperation that will be described below. The redundancy version (RV)field may include any one of 1, 2, 3 and 4. 1, 2, 3 and 4 are repeatedlyused in circular manner.

The uplink channels include a PUSCH, a PUCCH, an SRS (Sounding ReferenceSignal), and a PRACH (physical random access channel).

FIG. 6 shows a structure of an uplink subframe in 3GPP LTE.

Referring to FIG. 6, the uplink subframe can be divided into a controlregion and a data region. A physical uplink control channel (PUCCH) forcarrying uplink control information is allocated to the control region.A physical uplink shared channel (PUSCH) for carrying data is allocatedto the data region.

The PUCCH for one UE is allocated in an RB pair in a subframe. RBsbelonging to the RB pair occupy different subcarriers in each of a firstslot and a second slot. A frequency occupied by the RBs belonging to theRB pair to which the PUCCH is allocated changes at a slot boundary. Thisis called that the RB pair allocated to the PUCCH is frequency-hopped atthe slot boundary.

Since the UE transmits the uplink control information on a time basisthrough different subcarriers, a frequency diversity gain can beobtained. m is a location index indicating a logical frequency domainlocation of a RB pair allocated to a PUCCH in a subframe.

Examples of the uplink control information transmitted on a PUCCHinclude hybrid automatic repeat request (HARQ), acknowledgement(ACK)/non-acknowledgement (NACK), channel quality indicator (CQI)indicating a DL channel state, scheduling request (SR) which is a ULradio resource allocation request, etc.

The PUSCH is mapped to an uplink shared channel (UL-SCH) which is atransport channel. Uplink data transmitted through the PUSCH may be atransport block which is a data block for the UL-SCH transmitted duringa TTI. The transport block may be user information. In addition, theuplink data may be multiplexed data. The multiplexed data may beobtained by multiplexing the control information and a transport blockfor the UL-SCH.

<Carrier Aggregation>

A carrier aggregation system is now described.

A carrier aggregation system aggregates a plurality of componentcarriers (CCs). A meaning of an existing cell is changed according tothe above carrier aggregation. According to the carrier aggregation, acell may signify a combination of a downlink component carrier and anuplink component carrier or an independent downlink component carrier.

Further, the cell in the carrier aggregation may be classified into aprimary cell, a secondary cell, and a serving cell. The primary cellsignifies a cell operated in a primary frequency. The primary cellsignifies a cell which UE performs an initial connection establishmentprocedure or a connection reestablishment procedure or a cell indicatedas a primary cell in a handover procedure. The secondary cell signifiesa cell operating in a secondary frequency. Once the RRC connection isestablished, the secondary cell is used to provided an additional radioresource.

As described above, the carrier aggregation system may support aplurality of component carriers (CCs), that is, a plurality of servingcells unlike a single carrier system.

The carrier aggregation system may support a cross-carrier scheduling.The cross-carrier scheduling is a scheduling method capable ofperforming resource allocation of a PDSCH transmitted through othercomponent carrier through a PDCCH transmitted through a specificcomponent carrier and/or resource allocation of a PUSCH transmittedthrough other component carrier different from a component carrierbasically linked with the specific component carrier.

<EPDCCH (Enhanced Physical Downlink Control Channel)>

Meanwhile, a PDCCH is monitored in a limited region called a controlregion within a subframe, and a CRS transmitted in the entire band isused for demodulation of the PDCCH. As types of control information arediversified and an amount of control information is increased,flexibility of scheduling only with the existing PDCCH is lowered. Also,in order to reduce a burden due to CRS transmission, an enhanced PDCCH(EPDCCH) has been introduced.

FIG. 7 illustrates an example of a subframe having an EPDCCH.

A subframe may include zero or one PDCCH region 4100 and zero or morePEDCCH regions 420 and 430

The PEDCCH regions 420 and 430 are regions in which a wireless devicemonitors an EPDCCH. The PDCCH region 410 is positioned within a maximumof four preceding OFDM symbols, while the EPDCCH regions 420 and 430 maybe flexibly scheduled in subsequent OFDM symbols after the PECCH region410.

One or more EPDCCH regions 420 and 430 are designated in a wirelessdevice, and the wireless device may monitor an EPDCCH in the designatedEPDCCH regions 420 and 430.

The number/position/size of the EPDCCH regions 420 and 430 and/orinformation regarding a subframe for monitoring the PEDCCH may beprovided by a BS to the wireless device through an RRC message, or thelike.

In the PDCCH region 410, a PDCCH may be demodulated on the basis of aCRS. In the EPDCCH regions 420 and 430, a demodulation (DM) RS, ratherthan a CRS, may be defined to demodulate an EPDCCH. An associated DM RSmay be transmitted in the EPDCCH regions 420 and 430.

Each of the EPDCCH regions 420 and 430 may be used to perform schedulingon different cells. For example, an EPDCCH within the EPDCCH region 420may carry scheduling information for a primary cell and an EPDCCH withinthe EPDCCH region 430 may carry scheduling information for a secondarycell.

When an EPDCCH is transmitted in the EPDCCH regions 420 and 430 throughmultiple antennas, the same precoding as that of an DPCCH may be appliedto a DM RS within the EPDCCH regions 420 and 430.

Compared with a PDCCH which uses a CCE as a transmission resource unit,a transmission resource unit for an EPDCCH is called an enhanced controlchannel element (ECCE). An aggregation level (AL) may be defined by aresource unit for monitoring an EEPDCCH. For example, when 1 ECCE is aminimum resource for an EPDCCH, an AL may be defined as AL={1, 2, 4, 8,16}.

Hereinafter, an EPDCCH search space may correspond to an EPDCCH region.In the EPDCCH search space, one or more EPDCCH candidates may bemonitored in one or more ALs.

Hereinafter, resource allocation for an EPDCCH will be described.

The EPDCCH is transmitted using one or more ECCEs. Each ECCE includes aplurality of enhanced resource element groups (EREEGs). An ECCH mayinclude four eight EREGs according to a CP and a subframe type accordingto time division duplex (TDD) DL-UL. For example, in a normal CP, theECCE may include 4 EREGs, and in an extended CP, the ECCE may include 8EREGs.

A physical resource block (PRB) pair refers to two PRBs having the sameRB number in one subframe. The PRB pair refers to a first PRB of a firstslot and a second PRB of a second slot. In a normal CP, a PRB pairincludes 12 subcarriers and 14 OFDM symbols, and thus, the PRB pairincludes 168 source elements (REs).

The EPDCCH search space may be set as one or a plurality of PRB pairs.One PRB pair includes 16 EREGs. Thus, when an ECCE includes 4 EREGs, aPRB pair includes four ECCEs, and when an ECCE includes 8 EREGs, a PRBpair includes two ECCEs.

<Machine Type Communication (MTC)>

Meanwhile, hereinafter, the MTC will be described.

FIG. 8a illustrates an example of the machine type communication (MTC).

The machine type communication (MTC) represents information exchangethrough between MTC devices 100 through a base station 200 orinformation exchange between the MTC device 100 and an MTC server 700through the base station, which does not accompany human interaction.

The MTC server 700 is an entity which communicates with the MTC device100. The MTC server 700 executes an MTC application and provides an MTCspecific service to the MTC device.

The MTC device 100 as a wireless device providing the MTC may be fixedor mobile.

The service provided through the MTC has discrimination from a servicein communication in which human intervenes in the related art andincludes various categories of services including tracking, metering,payment, a medical field service, remote control, and the like. In moredetail, the service provided through the MTC may include electric meterreading, water level measurement, utilization of a monitoring camera,reporting of an inventory of a vending machine, and the like.

As peculiarities of the MTC device, since a transmission data amount issmall and uplink/downlink data transmission/reception often occurs, itis efficient to decrease manufacturing cost of the MTC device and reducebattery consumption according to the low data transmission rate. The MTCdevice is characterized in that mobility is small, and as a result, theMTC device is characterized in that a channel environment is not almostchanged.

Meanwhile, the MTC is also called Internet of Things (IoT). Accordingly,the MTC device may be called an IoT device.

FIG. 8b illustrates an example of cell coverage extension for an MTCdevice.

In recent years, it is considered that cell coverage of the base stationextends for the MTC device 100 and various techniques for the cellcoverage extension are discussed.

However, in the case where the coverage of the cell extends, when thebase station transmits a downlink channel to the MTC device positionedin the coverage extension area, the MTC device undergoes a difficulty inreceiving the downlink channel.

FIG. 9 is an exemplary diagram illustrating an example of transmitting abundle of downlink channels.

As known with reference to FIG. 9, the base station repeatedly transmitsthe downlink channel (for example, the PDCCH and/or PDSCH) to the MTCdevice positioned in the coverage extension area on multiple subframes(for example, N subframes). As described above, the downlink channelswhich are repeated on the multiple subframes are called a bundle of thedownlink channels.

Meanwhile, the MTC device receives the bundle of the downlink channelson the multiple subframes and decodes a part or the entirety of thebundle to increase decoding success rate.

FIGS. 10A and 10B are views showing examples of a subband for operationof an MTC device.

As one scheme for low cost of the MTC device, as shown in FIG. 10A,regardless of the system bandwidth of the cell, the MTC device may use asubband of about 1.4 MHz for example.

In this connection, the region of the subband for operation of the MTCdevice may be located in the central region (for example, six middlePRBs) of the system bandwidth of the cell as shown in FIG. 10A.

Alternatively, as shown in FIG. 10B, multiple subbands for the MTCdevices are allocated in one subframe for multiplexing between MTCdevices. Thus, the MTC devices may use different subbands. In thisconnection, most of the MTC devices may use other subbands rather thanthe central region (for example, middle six PRBs) of the cell's systemband.

Further, the MTC device operating on the reduced band may not properlyreceive the legacy PDCCH transmitted from the base station on the entiresystem band. Further, considering multiplexing with PDCCHs transmittedto other general UEs, it may not be desirable for the cell to transmitthe PDCCH for the corresponding MTC device in an OFDM symbol region forlegacy PDCCH transmission.

<Disclosure of the Present Description>

Accordingly, the disclosure of the present invention is to present asolution to solve these problems.

As one method of solving these problems, it is required to introduce acontrol channel for a MTC device which is transmitted in a subband inwhich a low-complexity/low-specification/low-cost MTC is operated.

Hereinafter, in the disclosure of the present invention, the MTC deviceoperated on a reduced bandwidth as a bandwidth reduced low complexity)is referred to as a LC device or bandwidth reduced low complexity (BL)device, in accordance with a low-complexitylow-capability/low-specification/low-cost. Herein, in accordance withthe disclosure of the present invention, a coverageextension/enhancement (CE) is divided into two modes. A first mode (oralso referred to as a CE mode A) is a mode in which a repetitivetransmission is not performed, or a small number of repetitivetransmission. A second mode (or also referred to as CE mode B) is a modein which a large number of repetitive transmission is allowed. As tooperating in any mode of the above two modes, it may be signaled to theLC device or the BL device. Herein, depending on the CE mode, parametersassumed by the LC device or the BL device for transmission/reception ofthe control channel/data channel may be different. Also, depending onthe CE mode, the DCI format which the LC device or the BL devicemonitors may be changed. However, some physical channels may berepeatedly transmitted the same number of times irrespective of the CEmode A and the CE mode B.

FIG. 11 shows an example of a control channel transmitted in a subbandin which an LC device/BL device operates.

As can be seen with reference to FIG. 11, when the LC device or the BLdevice does not operate using the entire system bandwidth of the cellbut the LC device or the BL device operates on any subband of the systembandwidth of the cell, the base station may transmit a control channelfor the BL device in the subband. This control channel may be repeatedlytransmitted on a plurality of subframes.

Such a control channel may be similar to the existing EPDCCH. That is,the control channel for the LC device or the BL device can be generatedusing the existing EPDCCH as it is. Or the control channel (or M-PDCCH)for the LC device or the BL device may be a modified form of theexisting PDCCH/EPDCCH.

Hereinafter, the control channel for the LC device or the BL device willbe referred to as MTC-EPDCCH or M-PDCCH. This MTC-EPDCCH or M-PDCCH maybe used for the LC device or BL device but may be used forlow-complexity/low-specification/low-cost UEs, or for coverage extensionor coverage enhancement coverage enhancement area.

However, there are some items to be considered when defining the M-PDCCHusing the existing EPDCCH.

Specifically, the RE mapping in the existing EPDCCH is performeddifferently depending on whether the corresponding subframe is a normaldownlink subframe or a special subframe. These factors include thefollowing:

EREG to RE Mapping

The RE mapping of EREG in the existing EPDCCH is as follows.

EREGs are used to define the mapping of EPDCCHs to REs. There are 16EREGs from 0 to 15 per PRB pair. All REs except the REs used to transmitthe DMRS in the PRB pair are first mapped in the frequency axisdirection in ascending order from 0 to 15 and then mapped in the timeaxis direction. All REs that are numbered i in the PRB pair are includedin the EREG with number i.

Since a different DMRS pattern is used in the special subframe than inthe normal downlink subframe, the EREG to RE mapping in the specialsubframe should be different from the EREG to RE mapping in the normaldownlink subframe.

ECCE to EREG Mapping

In the special subframe, the number of REs included in one RB is smallerthan that in the normal downlink subframe. In addition, the number ofEREGs in the ECCE may be changed depending on the special subframeconfiguration. For example, in the special subframe settings 3, 4 and 8,four EREGs are included in one ECCE, and eight special EREGs areincluded in one ECCE in special subframe settings 1, 2, 7, and 9.

EPDCCH to RE Mapping

In a special subframe, a maximum of two OFDM symbols may be used fortransmission of the PDCCH, while in the normal downlink subframe, amaximum of three OFDM symbols may be used for transmission of the PDCCH.Therefore, the position of the OFDM symbol in which the transmission ofthe EPDCCH starts in the normal downlink subframe and the specialsubframe may be changed. In this case, the same EPDCCH symbol may betransmitted on the different RE position in the special subframe and inthe normal downlink subframe.

Also, the aggregation levels (AL) which the UE monitors to receive theEPDCCH and the number of decoding candidates for each AL may bedifferent from between the normal downlink subframe and the specialsubframe. For example, in the case of the special subframe settings 3,4, and 8, the number of AL and AL decoding candidates to be monitoreddepending on case 1 (or case 3) is determined, and in the case of thespecial subframe settings 1, 2, 6, 7, 9, the number of monitoring ALsand the number of decoding candidates per AL are determined depending oncase 2. On the other hand, in the case of the normal downlink sub-frame,in the normal CP environment, decoding candidates per AL and the numbersof AL to be monitored depending on the case 1 or case 3 are determineddepending on DCI size and the number of RE resources etc. in the PRBcapable of transmitting EPDCCH.

The following table shows the EPDCCH candidates which the UE shouldmonitor for the case 1 and case 2 in one distributed EPDCCH-PRB-set.

TABLE 6 The number of EPDCCH candidates The number of EPDCCH candidatesM^((L)) _(p) for the case 1 M^((L)) _(p) for the case 2 N^(Xp) _(RB) L =2 L = 4 L = 8 L = 16 L = 32 L = 1 L = 2 L = 4 L = 8 L = 16 2 4 2 1 0 0 42 1 0 0 4 8 4 2 1 0 8 4 2 1 0 8 6 4 3 2 1 6 4 3 2 1

The following table shows the EPDCCH candidates which the UE shouldmonitor for the case 3 in one distributed EPDCCH-PRB-set.

TABLE 7 The number of EPDCCH candidates M^((L)) _(p) for the case 3N^(Xp) _(RB) L = 1 L = 2 L = 4 L = 8 L = 16 2 8 4 2 1 0 4 4 5 4 2 1 8 44 4 2 2

The following table shows the EPDCCH candidates which the UE shouldmonitor for the case 1 and case 2 in one local EPDCCH-PRB-set.

TABLE 8 The number of The number of EPDCCH candidates EPDCCH candidatesM^((L)) _(p) for the case 1 M^((L)) _(p) for the case 2 N^(Xp) _(RB) L =2 L = 4 L = 8 L = 16 L = 1 L = 2 L = 4 L = 8 2 4 2 1 0 4 2 1 0 4 8 4 2 18 4 2 1 8 6 6 2 2 6 6 2 2

The following table shows the EPDCCH candidates which the UE shouldmonitor for the case 3 in one local EPDCCH-PRB-set.

TABLE 9 The number of EPDCCH candidates M^((L)) _(p) for the case 3N^(Xp) _(RB) L = 1 L = 2 L = 4 L = 8 2 8 4 2 1 4 6 6 2 2 8 6 6 2 2

As described above, in the existing EPDCCH, its mapping scheme isperformed differently depending on whether the corresponding subframe isa special subframe or a normal downlink subframe. Therefore, it isdifficult to define the M-PDCCH using the existing EPDCCH as it is.

Therefore, the following solutions will be presented.

I. ECCE Index Corresponding to M-PDCCH Candidate in Special Subframe

As described above, the number of AL and Decoding candidates per ALexisting in the normal downlink subframe and in the special subframe maybe changed. In this case, when M-PDCCHs having L ALs are repeatedlytransmitted on a plurality of (e.g., R) subframes, in the specificnormal downlink subframe k, the ECCE indices #n₁, #n₂, . . . , #n_(L)may be used for transmission of the M-PDCCH. Specifically, in thespecific normal downlink subframe k, the ECCE indexes #n, # n+1, . . . ,# n+L may be used for transmission of the M-PDCCH. In this case, morespecifically, the indexes of the ECCEs (constituting the M-PDCCHcandidate) in which the M-PDCCH is transmitted for each subframe may bethe same. Here, proposed are ECCEs (constituting M-PDCCH candidates) inwhich M-PDCCH is transmitted in the special subframe.

FIG. 12 is a flow chart illustrating a method according to thedisclosure of the present description.

Referring to FIG. 12, the LC device or the BL device receives the SIB.The SIB includes a special subframe configuration and valid subframeinformation. The valid subframe information may specify a specialsubframe based on a specific special subframe configuration as a validsubframe.

In addition, the LC device or the BL device receives configurationinformation for repetition of the M-PDCCH.

Then, the LC device or the BL device determines a sub-frame to receivethe repetition of the M-PDCCH. In this case, the special subframe basedon the specific TDD special subframe configuration may be determined tobe excluded from receiving the repetition of the M-PDCCH.

The LC device or the BL device may receive the repetition of the M-PDCCHon the determined plurality of subframes excluding the special subframe.

Hereinafter, the details will be described.

I-1. Skip Special Sub-Frame

When the M-PDCCH is transmitted on a plurality of subframes (or when aresource for one M-PDCCH candidate includes a plurality of subframes),the subframe in which the M-PDCCH is transmitted may be defined toinclude only the normal downlink subframe (excluding the specialsubframe). Or if there is a special subframe among the subframes inwhich the M-PDCCH is transmitted, then the LC device or the BL devicemay assume that the M-PDCCH is not transmitted on the correspondingsubframe.

I-2. Determine the ECCE Index to Use Based on the Normal DownlinkSubframe

The ECCE to EREG mapping, and EREG to RE mapping in the special subframemay follow a mapping in the special subframe. In this case, when theM-PDCCH is repeatedly transmitted on a plurality of subframes (or when aresource for one M-PDCCH candidate includes a plurality of subframes),the ECCE resources to be use for the transmission of M-PDCCH in thespecial subframe may be determined based on the normal downlinksubframe. That is, even if the corresponding subframe is the specialsubframe, the LC device or the BL device may determine the ECCE indexes#n₁, #n₂, . . . , #n_(L) used for transmission of the M-PDCCH in thesubframe #k, assuming the corresponding subframe as the normal downlinksubframe. Or, even if the corresponding subframe is a special subframe,the LC device or the BL device may determine the ECCE resources (ECCEindexes #n₁, #n₂, . . . , #n_(L)) constituting the M-PDCCH candidate inthe subframe #k, assuming the corresponding subframe as the normaldownlink subframe. That is, the indexes of the ECCE resources in whichone M-PDCCH is transmitted (or constitute one M-PDCCH candidate) may bedetermined identically in the normal downlink subframe and the specialsubframe. In this case, if the indexes of the ECCEs (constituting theM-PDCCH candidate) to which the M-PDCCH is transmitted for each subframeare the same, then the M-PDCCH may be also transmitted using the sameECCE indexes in the special subframe.

In this case, the ECCE (ECCE index) existing in the normal downlinksubframe may not exist in the special subframe. For example, in the caseof special subframe settings 1, 2, 7, and 9, since one ECCE includeseight EREGs, the number of ECCEs existing in the corresponding subframeis reduced to half compared with the normal downlink subframe. If theECCE index to be used for transmission of the M-PDCCH does not exist inthe special subframe, then the M-PDCCH may be transmitted excluding thecorresponding ECCE resource. That is only ECCEs existing in the specialsub-frame, of the ECCEs (ECCE indexes) constituting one M-PDCCHcandidate, may be used as ECCE resources constituting the correspondingM-PDCCH candidate in the special sub-frame.

Or if the ECCE index to be used for transmission of the M-PDCCH does notexist in the special sub-frame, then the special sub-frame may not beused to transmit the M-PDCCH. That is, when all the ECCE resources (ECCEindex) to be used for transmission of the M-PDCCH exist in the specialsub-frame, the M-PDCCH may also be transmitted in the special sub-frame.Or, if all ECCEs (ECCE indexes) constituting one M-PDCCH candidate existin only the special sub-frame, then the corresponding ECCEs may be usedas the ECCE resources constituting the corresponding M-PDCCH candidatein the special sub-frame.

I-3. Mapping Based on Normal Downlink Sub-Frame

The ECCE to EREG mapping and/or the EREG to RE mapping for the M-PDCCHin the special subframe may follow the mapping in the normal downlinksubframe. If the EREG to RE mapping for the M-PDCCH follows the mappingof the normal downlink subframe, then the transmission of the DMRS mayalso be transmitted depending on the DMRS transmission resources in thenormal downlink subframe. Or, the DMRS follows the transmission REresource in the special subframe, and the EREG to RE mapping may beperformed based on the DMRS RE location in the normal downlink subframe.In this case, if the transmission resource of the M-PDCCH conflicts withthe transmission resource of the DMRS, then rate-matching or puncturingmay be performed on the transmission of the M-PDCCH to the correspondingRE resource. When the ECCE to EREG mapping for the M-PDCCH follows themapping of the normal downlink subframe, the number of EREGs included inthe ECCE may follow the number of EREGs included in the ECCE in thenormal downlink subframe (having the same CP length). This is to keepthe number of ECCEs existing in the normal downlink subframe and thespecial subframe identically.

In this case, when the M-PDCCH is transmitted on a plurality ofsubframes (or when a resource for one M-PDCCH candidate includes aplurality of subframes), the ECCE resources used for transmission of theM-PDCCH in the special subframe may be determined based on the normaldownlink subframe. That is, assuming the corresponding subframe as thenormal downlink subframe, the ECCE index #n₁, #n₂, . . . , #n_(L) usedfor transmission of the M-PDCCH in the subframe #k may be determined.Or, assuming the corresponding subframe as the normal downlink subframe,the ECCE resources (ECCE index #n₁, #n₂, . . . , #n_(L)) constitutingthe M-PDCCH candidate in the subframe #k may be determined. That is, theindex of the ECCE resource to which one M-PDCCH is transmitted (orconstitute one M-PDCCH candidate) may be determined in the normaldownlink subframe and the special subframe identically. In this case, ifthe indexes of the ECCEs (constituting the M-PDCCH candidate) to whichthe M-PDCCH is transmitted are the same, then the M-PDCCH may be alsotransmitted using the same ECCE indexes in the special subframe.

In the existing EPDCCH, the number of an aggregation level (AL) and thenumber of Decoding candidates per AL existing in the EPDCCH USS on thespecific subframe is determined differently depending on a case in whicheach subframe is corresponded to (that is, any case of cases 1, 2 and3).

For example, when a subframe in which EPDCCH is transmitted belongs tothe case 3 is a general case, if a subframe in which EPDCCH istransmitted belongs to the case 1, then the number of EREGs included inthe ECCE is four, which is the same as the general case, but the valueof the ALs included in the search space is doubled as compared with thegeneral case. That is, for example, AL 1, 2, 4, 8, and 16 are supportedin the general case, but AL 2, 4, 8, 16, and 32 are supported in thecase 1.

In addition, if the subframe in which the EPDCCH is transmitted belongsto the case 2, then the number of EREGs included in the ECCE is 8, whichis twice as large as that in the general case. Therefore, since thenumber of ECCEs existing in the PRB is reduced to half as compared withthe general case, the number of AL and decoding candidates which may besupported in the corresponding subframe is reduced.

When the LC device or the BL device is located in the basic coverage orcoverage extension area shown in FIG. 8B, if the base station repeatedlytransmits the M-PDCCH, or transmits it without repetition, according tothe existing standard, cases to which the subframe used for transmissionbelongs may be different. Therefore, depending on the subframe in whichthe M-PDCCH is transmitted, the problem that the number of AL andDecoding candidates per AL and/or EREG included in ECCE may be changed,may be occurred.

To solve this problem, operating as follows is proposed.

First, in the case of basic coverage (i.e., normal coverage), or whenthe number of repetitive transmissions of the M-PDCCH is 1, it may be asfollows.

Option 1. Depending on whether the corresponding subframe is a normaldownlink subframe or a special subframe, such as in an existing EPDCCH,a special subframe configuration, a DCI format, a system bandwidth, a CPlength, and/or the number of REs to which the PDCCH can be transmitted,the case is divided into for the M-PDCCH, for each case, the number ofAL and Decoding candidates per AL constituting the M-PDCCH search spaceand/or the number of EREGs included in the ECCE may be changed.

Option 2. In all subframes, the ECCE includes four EREGs, and the numberof AL and Decoding candidates per AL constituting the M-PDCCH searchspace may be the same.

As for having a normal CP, in case of Small/Medium/High coverageenhancement or in case of the number of M-PDCCH repetitivetransmission >1, it may be as follows.

Option 1. The LC device or the BL device may be treated as an invalidsubframe for transmission of the M-PDCCH on the subframe belonging tothe case 1 and/or case 2. In this case, the transmission of the M-PDCCHmay not be performed in the corresponding subframe. In addition, in thiscase, the LC device or the BL device can exclude the correspondingsubframe from counting the number of repetitions of the M-PDCCH. Or, inthis case, even if the base station does not actually transmit theM-PDCCH on the corresponding subframe, the LC device or the BL devicemay count the corresponding subframe as the number of repetitions of theM-PDCCH.

Option 2: In case of a subframe belonging to the case 2 (a specialsubframe by special subframe settings 1, 2, 6, 7 and 9 with the normalCP), the LC device or the BL device may treat that the correspondingsubframe is an invalid subframe for the transmission of the M-PDCCH. Inthis case, the base station may not perform transmission of the M-PDCCHon the corresponding subframe. Thus, even if the base station does notactually transmit the M-PDCCH on the corresponding subframe, the LCdevice or the BL device may count the subframe as the number ofrepetitions of the M-PDCCH. When the M-PDCCH is repeatedly transmitted,the M-PDCCH may be transmitted through the same ECCE resource in allsubframes, except for an invalid subframe.

Option 3. The ECCE in all subframes may contain 4 EREGs. When the basestation repeatedly transmits the M-PDCCH, the M-PDCCH may be transmittedthrough the same ECCE resource on all subframes.

Option 4. In the case 2 (special subframe according to special subframesettings 1, 2, 6, 7, 9 with normal CP) as in the existing EPDCCH, thenumber of EREGs included in the ECCE may be 8. In this case, when thebase station repeatedly transmits the M-PDCCH, the M-PDCCH may betransmitted through ECCEs having the same ECCE index in all subframes.In this case, when the number of EREGs included in the ECCE is 8 and theECCE index at which the M-PDCCH is to be transmitted is not all orpartially present, 1) the base station may skip transmission of theM-PDCCH on the corresponding subframe. Accordingly, even if thecorresponding subframe is not used for transmission of the M-PDCCH, theLC device or the BL device may count the corresponding subframe as thenumber of repetitions of the M-PDCCH. Alternatively, the base stationcan perform M-PDCCH transmission using only existing ECCE resources,among the ECCEs constituting the decoding candidate on the correspondingsubframe. Accordingly, even if the base station does not actuallytransmit the M-PDCCH in the corresponding subframe or transmits usingonly some ECCE resources, the LC device or the BL device may count thecorresponding subframe as the number of repetitions of the M-PDCCH.

When the number of repetitions of transmissions of the M-PDCCH isspecifically referred to as R, the base station transmits the M-PDCCHusing the special subframe for R=1, and does not use the specialsubframe for transmitting of the M-PDCCH for R>1. In this case, even ifthe special subframe is not used for transmission of the M-PDCCH, if thecorresponding subframe is configured as a valid subframe by the SIB,then the LC device or the corresponding subframe may be counted as therepetition number of the M-PDCCH.

Or specifically, the base station may not use the special subframes fortransmission of the M-PDCCH for all Rs. In this case, even if thespecial subframe is configured as a valid subframe by the SIB, the LCdevice or the BL device may not count the special subframe as the numberof repetitions of the M-PDCCH.

Specifically, for R=1, the M-PDCCH and the DMRS may be transmitted so asto follow the EREG to RE mapping and the DMRS pattern of the existingEPDCCH in the special subframe. However, for R>1, the M-PDCCH and theDMRS may be transmitted so as to follow the EREG to RE mapping and theDMRS pattern in the normal downlink subframe.

Or, in the CE mode A, the M-PDCCH and DMRS may be transmitted to followthe EREG to RE mapping and DMRS pattern of the existing EPDCCH. However,in case of the CE mode B, the M-PDCCH and the DMRS may be transmitted soas to follow the EREG to RE mapping and the DMRS pattern in the normaldownlink subframe.

These above techniques have the advantage of facilitating I/Qsymbol-level combined decoding of the M-PDCCH for R>1.

The above description includes that the different methods among theabove-mentioned proposed methods are applied depending on the number ofrepetitions of the M-PDCCH or depending on the CE mode (i.e., the CEmode A or B).

II. M-PDCCH Transmission for I/Q Symbol-Level Combined Decoding

When a base station transmits an M-PDCCH on a plurality of subframes, inthe case of an LC device or a BL device in which the channel does notchange rapidly, it demodulates the received data by combining an I/Qsymbol level (or combining an RE level), thereby improving the receptionperformance. In this case, in order for the LC device or the BL deviceto demodulate the M-PDCCH transmitted on a plurality of subframes bycombining (symbol level), it is preferable that the same symbols aremapped on the same RE resource, and thus they experience the samechannel environment. Therefore, when the M-PDCCH is repeatedlytransmitted on a plurality of subframes, the M-PDCCH may be transmittedusing the same RE mapping on a plurality of subframes. Therefore, ifthere is a special subframe among the subframes in which the M-PDCCH istransmitted, then the M-PDCCH is required to be transmitted through thesame RE mapping as the normal downlink subframe in the special subframe.

To this end, it is proposed in the present invention that the ECCE toEREG mapping and the EREG to RE mapping in the special subframe followthe mapping in the normal downlink subframe. If the EREG to RE mappingfollows the mapping of the normal downlink subframe, then thetransmission of the DMRS may also be transmitted depending on the DMRStransmission resources in the normal downlink subframe. Or, the DMRSfollows the transmission RE resource in the special subframe, and theEREG to RE mapping may be performed based on the DMRS RE location in thenormal downlink subframe. In this case, if the transmission resource ofthe M-PDCCH and the transmission resource of the DMRS collide, then arate-matching or puncturing may be performed on the transmission of theM-PDCCH to the corresponding RE resource. When the ECCE to EREG mappingfollows the mapping of the normal downlink subframe, the number of EREGsincluded in the ECCE may follow the number of EREGs included in the ECCEin the normal downlink subframe (having the same CP length). This is tokeep the number of ECCEs existing in the normal downlink subframe andthe special subframe identically.

In addition, in order to apply the same RE mapping as the normaldownlink subframe in the special subframe, the position of the M-PDCCHtransmission start OFDM symbol in the special subframe (i.e., the numberof OFDM symbols to which the existing PDCCH is transmitted) may beassumed to be the same as the position of the M-PDCCH transmission startOFDM symbol in the frame (i.e., the number of OFDM symbols in which theexisting PDCCH is transmitted).

In this case, in order to enable efficient I/Q symbol combining when theM-PDCCH is repeatedly transmitted on a plurality of subframes (or when aresource for one M-PDCCH candidate includes a plurality of subframes),in the subframes for performing I/Q symbol combining or in all subframesin which the M-PDCCH is transmitted, the indexes of the ECCEs(constituting the M-PDCCH candidate) in which the M-PDCCH is transmittedis required to be the same. In this case, the M-PDCCH may be transmittedin the special subframe using the same ECCE indices as those in thenormal downlink subframe.

The embodiments of the present invention described hereto may beimplemented by various means. For example, embodiments of the presentinvention may be implemented by hardware, firmware, software, or acombination thereof. More specifically, the description will be madewith reference to a figure.

FIG. 13 is a block diagram illustrating a wireless communication systemin which a disclosure of the present description is implemented.

A base station 200 includes a processor 201, a memory 202 and atransceiver (or an RF (radio frequency) unit) 203. The memory 202 isconnected to the processor 51, and stores various information fordriving the processor 201. The transceiver (or an RF unit) 203 isconnected to the processor 201, and transmits and/or receives radiosignals. The processor 2011 implements proposed functions, processesand/or methods. In the above embodiment, the operation of the basestation 200 can be implemented by the processor 201.

A wireless device (e.g., a LC device or a BL device) 100 includes aprocessor 101, a memory 102 and a transceiver (or an RF unit) 103. Thememory 102 is connected to the processor 101, and stores variousinformation for driving the processor 101. The RF unit 103 is connectedto the processor 101, and transmits and/or receives radio signals. Theprocessor 101 implements proposed functions, processes and/or methods.

The processor may include Application-Specific Integrated Circuits(ASICs), other chipsets, logic circuits, and/or data processors. Thememory may include Read-Only Memory (ROM), Random Access Memory (RAM),flash memory, memory cards, storage media and/or other storage devices.The RF unit may include a baseband circuit for processing a radiosignal. When the above-described embodiment is implemented in software,the above-described scheme may be implemented using a module (process orfunction) which performs the above function. The module may be stored inthe memory and executed by the processor. The memory may be disposed tothe processor internally or externally and connected to the processorusing a variety of well-known means.

In the above exemplary systems, although the methods have been describedon the basis of the flowcharts using a series of the steps or blocks,the present invention is not limited to the sequence of the steps, andsome of the steps may be performed at different sequences from theremaining steps or may be performed simultaneously with the remainingsteps. Furthermore, those skilled in the art will understand that thesteps shown in the flowcharts are not exclusive and may include othersteps or one or more steps of the flowcharts may be deleted withoutaffecting the scope of the present invention.

1. A method for receiving a signal for a downlink control channel, themethod performed by a device and comprising: if the device is configuredwith a repetition of the downlink control channel, determining aplurality of subframes for receiving the repetition of the downlinkcontrol channel, wherein a special subframe based on a specific timedivision duplex (TDD) special subframe configuration is determined to beexcepted for receiving the repetition of the downlink control channel,and wherein the excepted special subframe includes one or more specialsubframes with a special subframe configuration 1, 2, 6, 7 or 9 innormal cyclic prefix (CP); and receiving the signal for the downlinkcontrol channel repeated over the determined plurality of subframesexcept for the special subframe.
 2. The method of claim 1, wherein aspecial subframe other than the excepted special subframe is determinedto be used for receiving the repetition of the downlink control channel.3. The method of claim 1, wherein the excepted special subframe includesa different number of enhanced control channel elements (ECCEs) from anumber of ECCEs of a normal downlink subframe.
 4. The method of claim 1,wherein a special subframe other than the excepted special subframeincludes different numbers of enhanced resource element groups (EREGs)per a ECCE according to a cyclic prefix (CP) length.
 5. (canceled) 6.The method of claim 1, further comprising: receiving a systeminformation block (SIB) for configuring the special subframe as a validsubframe.
 7. The method of claim 6, wherein if the special subframe isconfigured as the valid subframe, although the special subframe isexcepted for receiving the repetition of the downlink control channel,the excepted special subframe is used for counting the number of validsubframes.
 8. The method of claim 1, wherein the device is alow-capability (LC) device, a low-cost (LC) device or a bandwidthreduced device.
 9. A device for receiving a signal for a downlinkcontrol channel, comprising: a processor configured to determine aplurality of subframes for receiving a repetition of the downlinkcontrol channel, if the device is configured with the repetition of thedownlink control channel, wherein a special subframe based on a specifictime division duplex (TDD) special subframe configuration is determinedto be excepted for receiving the repetition of the downlink controlchannel, and wherein the excepted special subframe includes one or morespecial subframes with a special subframe configuration 1, 2, 6, 7 or 9in normal cyclic prefix (CP); and a transceiver controlled by theprocessor and configured to receive the signal for the downlink controlchannel repeated over the determined plurality of subframes except forthe special subframe.
 10. The device of claim 9, wherein a specialsubframe other than the excepted special subframe is determined to beused for receiving the repetition of the downlink control channel. 11.The device of claim 9, wherein the excepted special subframe includes adifferent number of enhanced control channel elements (ECCEs) from anumber of ECCEs of a normal downlink subframe.
 12. The device of claim9, wherein a special subframe other than the excepted special subframeincludes different numbers of enhanced resource element groups (EREGs)per a ECCE according to a cyclic prefix (CP) length.
 13. (canceled) 14.The device of claim 9, wherein the processor is further configured to:use the excepted special subframe for counting the number of validsubframes, if the special subframe is configured as the valid subframe,although the special subframe is excepted for receiving the repetitionof the downlink control channel.